This group has continued its study of sequence-specific DNA-binding proteins in Drosophila, with focus on transcription factors regulating heat shock genes and the segmentation gene fushi tarazu, ftz. Three transcription factors: heat shock factor (HSF), FTZ-F1, and FTZ-F2 (now referred to as tramtrack), previously cloned in the laboratory have been expressed in E. coli, and the recombinant proteins have been utilized for biochemical studies and for the preparation of antibodies. The antibodies have been employed to determine the subcellular distribution of the transcription factors. In addition, a human heat shock transcription factor has been cloned by PCR using local amino acid identities between the Drosophila and yeast HSF protein sequences. The cloning of a human HSF paves the way for a detailed study of the induction of this important physiological response in mammalian cells.